The soybean is the one of the few plant protein sources that provides all eight essential amino acids. Soy protein is of the highest quality, equal to that of meat and dairy products, but without the cholesterol and high levels of saturated fat. In addition, the soybean has a higher amount of protein than other beans. Research has revealed many possible health benefits that may be achieved from the consumption of food products containing soy protein. The bioactive molecules occurring naturally in soy protein have antioxidant activities, which enhance the immune system, the body's defense against a wide range of diseases. For example, soy protein may play a role in the reduction of the risk of developing cardiovascular disease, including preventing heart attack, stroke, and high blood pressure. Soy protein, which is contained within soya fiber particulates, may also play a role in the reduction of the risk of developing kidney disease, various cancers and diabetes. Soy protein may also help protect against the development of osteoporosis and promote weight management. Because of these and other potential health effects, the commercial demand for soya fiber particulates is expected to rise rapidly.
Soymilk, an aqueous extraction of soybeans, is used as a base in a wide variety of products. There are already a few reported processing techniques used in the manufacture of soymilk. A traditional method for soymilk production involves cleaning and then soaking whole, undehulled soybeans in cold water, rinsing the soaked soybeans, grinding the rinsed soybeans with additional fresh water into a coarse slurry, heating and then centrifuging the slurry, retaining the soluble soymilk fraction and disposing of the okara residue, also described as soymilk pulp or cell wall debris.
One disadvantage of traditional methods for soymilk production is the presence of an undesirable beany flavor, odor, and color. In order to improve the flavor of soymilk, alternate methods include heating and/or blanching for the inactivation of the enzymes that are responsible for the undesirable beany flavor and subsequent extraction of soluble constituents. For example, U.S. Pat. No. 4,039,696 describes a process for preparing a milk-like product from whole soybeans by hot aqueous alkaline blanching and centrifugation. U.S. Pat. No. 4,971,825 describes a process for producing soybean milk which involves crushing, rather than grinding, soybeans in aqueous hot medium followed by soy protein extraction. U.S. Pat. No. 4,992,294 discloses a method of producing soybean milk by boiling soybeans and straining the boiled solution. U.S. Pat. No. 5,945,151 describes a process for producing a soymilk which involves heating a soybean paste. U.S. Pat. No. 4,186,218 describes a process of improving denatured soy protein by superheating and/or alcohol extraction.
Other methods for eliminating undesirable odors from soymilk include fermentation. U.S. Pat. No. 3,971,843 describes a process for eliminating a bean odor from a soymilk by fermentation and distillation under reduced pressure. U.S. Pat. No. 4,664,919 describes a process for producing a liquid-like lactic acid soymilk drinks by inoculating filtered pulverized soybeans with Streptococcus sojalactis bacterium.
Soymilk produced according to traditional methods has a grainy texture. Occasionally, this grainy texture is desirable. For example, U.S. Pat. No. 6,413,557 describes a process for preparing a textured soya beverage which includes blending soaked, rinsed, and cooked soybeans with loose soybean hulls. However, a soymilk composition with a smooth texture and pleasant mouthfeel is usually preferable. In order to obtain a soymilk with a smooth texture, alternate methods include the addition of enzymes to soybeans to degrade proteinaceous, carbohydrate, and cellulosic constituents, preventing sedimentation. For example, U.S. Pat. No. 3,941,890 describes a process for preparing soymilk from dehulled soybeans by microwaving and adding suitable enzymatic material. U.S. Pat. No. 4,378,376 describes a process for producing a simulated milk protein product by forming a neutralized aqueous slurry of a soya protein material and dairy whey and then reacting the slurry with a proteolytic enzyme. Other methods for obtaining a soymilk with a smooth texture include multiple or extensive grinding steps. For example, U.S. Pat. No. 5,807,602 describes a process for making a finely divided soya product based on continuous milling, superheating and flash evaporation. This method obtains soya particles wherein 90% have a diameter of less than 85 microns and 50% have a diameter of less than 40 microns. U.S. Pat. No. 4,194,018 describes a process of preparing a soya composition from soybeans yielding particulate in which the largest dimension does not exceed 40 to 300 microns.
Finally, another disadvantage of traditional methods for soymilk production is that the full nutritional quality of the soybean is not maximized. In order to improve the nutritional quality of soymilk, alternate methods include the use of acid or acid salt to process soybeans; specifically to chelate various soybean components. For example, U.S. Pat. No. 6,322,846 describes a process for preparing soymilk and beverage compositions from whole soybeans which involves the addition of at least one of an acid and/or an acid salt. U.S. Pat. No. 4,389,425 describes a process for preparing a bovine milk substitute which includes grinding soybeans in the presence of an acidified water solution followed by homogenization, desludging, and extraction.
Other methods for improving the nutritional quality of soymilk involve extraction and/or filtration. For example, U.S. Pat. No. 3,995,071 describes a process based on the aqueous extraction of defatted soy flakes, basefication, and the removal of insolubles. U.S. Pat. No. 4,091,120 describes a process for preparing soya protein beverages by ultrafiltration purification and precipitation.
However, all of these reported processes are unable to produce a soya fiber particulate that has, simultaneously, a very smooth texture, a high nutritional value and lacks a beany flavor. For example, while the process disclosed in U.S. Pat. No. 4,194,018 produces a soya composition of a somewhat improved texture, the largest dimension of the product does not exceed 50 to 300 microns, meaning that the composition still has a grainy mouthfeel and lacks the stability for the prevention of sedimentation of the soy fiber particulate during storage. Therefore, there is a great need for improved, economical processes that provide very smooth soya fiber particulates.